Biosynthesis of photoreceptor cell membranes is being studied in Xenopus laevis, Rana pipiens, and bovine retinas by new immunocytochemical ultrastructural techniques. Pathways of transport of newly synthesized rhodopsin from rough endoplasmic reticulum and Golgi apparatus to the apical plasma membrane near the connecting cilium have been clarified. Vesicles bearing newly synthesized rhodopsin pass between mitochondria in the ellipsoid to this site where they fuse and deliver rhodopsin for passage via the plasma membrane of the connecting cilium to the base of the rod outer segment. A large membrane protein (Mr 290,000) is localized not only on incisures and margins of red rods but also to margins of green rods and cone outer segments and to short incisures of green rods. Quantitative morphometric analysis of antibody labeling density is permitting a quantitative analysis of membrane protein distribution in photoreceptor cells.